The present invention is related to a type of integrated circuit. Note specifically, the present invention is related to a differential-difference current conveyor using MOS devices and to applications of the differential-difference current conveyor, such as a filter circuit or an integrator circuit.
The differential-difference amplifier, widely used in op-amp circuits, is a fundamental amplifier circuit applied to integrated circuits. The differential-difference amplifier, formed by at least two BJT or MOS differential pairs, has several advantages, such as a reduction of the number of passive devices requiring matching, and a simplified design process.
In view of current technology, the conventional differential-difference amplifier still has many drawbacks and requires further improvement. First, like the conventional op-amp circuit, performance of the differential-difference amplifier is limited by its finite gain-bandwidth product, so that it is unsuitable for application in high frequency circuits. In addition, in an integrator circuit formed by the differential-difference amplifier, it is necessary to float a resistor or capacitor, which produces instability when incorporated into an integrated circuit.
However, a device called a current conveyor is quite appropriate for use in high-frequency circuits. The principle and performance of the current conveyor have been disclosed in U.S. Pat. No. 5,124,666.
In view of the disadvantages of the conventional technology described above, we provide a novel device, a differential-difference current conveyor, to solve these problems. The first object of the present invention is to provide a device, which has a superior finite gain-bandwidth product, and as a result, is appropriate for application in high frequency circuits.
The second object of the present invention is the use of the device as a building block of an integrator circuit, which does not require a floating resistor or capacitor and is well-suited for manufacture as an integrated circuit.
The third object of the present invention is to provide the device as a component in an integrator circuit, which can receive a number of input signals. More explicitly, the integrator circuit conducts a multiple input integration operation.
The fourth object of the present invention is to provide the device in a filter circuit, which has superior frequency response in comparison to prior art filter circuits.